Noise (signal processing)

Types of noise

• Additive noise, gets added to the unintended signal
• * White noise
• ** Additive white Gaussian noise
• * Black noise
• * Gaussian noise
• * Pink noise or flicker noise, with 1/f power spectrum
• * Brownian noise, with 1/f² power spectrum
• * Contaminated Gaussian noise, whose PDF is a linear mixture of Gaussian PDFs
• * Power-law noise
• * Cauchy noise
• Multiplicative noise, multiplies or modulates the intended signal
• Quantization error, due to conversion from continuous to discrete values
• Poisson noise, typical of signals that are rates of discrete events
• Shot noise, e.g. caused by static electricity discharge
• Transient noise, a short pulse followed by decaying oscillations
• Burst noise, powerful but only during short intervals
• Phase noise, random time shifts in a signal

  Noise in specific kinds of signals

• Noise, such as "hiss" or "hum", in audio signals
• * Background noise, due to spurious sounds during signal capture
• * Comfort noise, added to voice communications to fill silent gaps
• * Electromagnetically induced noise, audible noise due to electromagnetic vibrations in systems involving electromagnetic fields
• Noise, such as "snow"
• Noise, such as "static", in radio transmissions
• Image noise, affects images, usually digital ones
• * Salt and pepper noise or spike noise, scattered very dark or very light pixels
• * Fixed pattern noise, that is tied to pixel sensors
• * Shadow noise, made visible by increasing brightness or contrast
• * Speckle noise, typical of radar imaging and interferograms
• * Film grain in analog photography
• * Compression artifacts or "mosquito noise" around edges in JPEG and other formats
• Noise in electrical signals
• * Johnson–Nyquist noise, in semiconductors
• * Quantum noise
• * Quantum 1/f noise, a disputed theory about quantum systems
• * Generation-recombination noise, in semiconductor devices
• * Oscillator phase noise, random fluctuations of the phase of an oscillator
• * Barkhausen effect or Barkhausen noise, in the strength of a ferromagnet
• * Spectral splatter or switch noise, caused by on/off transmitter switching
• * Ground noise, appearing at the ground terminal of audio equipment
• Synaptic noise, observed in neuroscience
• Neuronal noise, observed in neuroscience
• Transcriptional noise in the transcription of genes to proteins
• Cosmic noise, in radioastronomy
• Phonon noise in materials science
• Internet background noise, packets sent to unassigned or inactive IP addresses
• Fano noise, in particle detectors
• Mode partition noise in optical cables
• Seismic noise, spurious ground vibrations in seismology
• Cosmic microwave background, microwave noise left over from the Big Bang

  Measures of noise in signals

• Dynamic range, often defined by inherent noise level
• Signal-to-noise ratio, ratio of noise power to signal power
• * Peak signal-to-noise ratio, maximum SNR in a system
• * Signal to noise ratio, for images
• * Carrier-to-noise ratio, the signal-to-noise ratio of a modulated signal
• Noise power
• Noise figure
• Noise-equivalent flux density, a measure of noise in astronomy
• Noise floor
• Noise margin, by how much a signal exceeds the noise level
• Reference noise, a reference level for electronic noise
• Noise spectral density, noise power per unit of bandwidth
• Noise temperature
• Effective input noise temperature
• Noise-equivalent power, a measure of sensitivity for photodetectors
• Relative intensity noise, in a laser beam
• Antenna noise temperature, measure of noise in telecommunications antenna
• Received noise power, noise at a telecommunications receiver
• Circuit noise level, ratio of circuit noise to some reference level
• Channel noise level, some measure of noise in a communication channel
• Noise-equivalent target, intensity of a target when the signal-to-noise level is 1
• Equivalent noise resistance, a measure of noise based on equivalent resistor
• Carrier-to-receiver noise density, ratio of received carrier power to receiver noise
• Carrier-to-noise-density ratio,
• Spectral signal-to-noise ratio
• Antenna gain-to-noise temperature, a measure of antenna performance
• Contrast-to-noise ratio, a measure of image quality
• Noise print, statistical signature of ambient noise for its suppression
• Equivalent pulse code modulation noise, measure of noise by comparing to PCM quantization noise

  Technology for noise in signals

• Noise shaping
• Antenna analyzer or noise bridge, used to measure the efficiency of antennas
• Noise gate
• Noise generator, a circuit that produces a random electrical signal
• Radio noise source used to calibrate radiotelescopes
• Friis formulas for the noise in telecommunications
• Noise-domain reflectometry, uses existing signals to find cable faults
• Noise-immune cavity-enhanced optical heterodyne molecular spectroscopy